This proposed research will seek to define the role of cell-mediated immunity (CMI) and the secretory IgA immune system in the establishment of experimental periodontal disease in gnotobiotic rats. We have proposed to explore the nature of these roles utilizing a series of experiments in which CMI or the IgA system will be enhanced or ablated. The research plan has six major directions for study: (1) Enhanced CMI by antigen injection; intact IgA. (2) Ablated CMI and reduced IgA in neonatally thymectomized rats. (3) Ablated IgA using anti-heavy chain reagents with intact CMI. (4) Ablated CMI, reduced IgA in neonatally thymectomized rats with serum IgG antibody stimulated by systemic injection. (5) Enhanced IgA, by antigen feeding, without alteration of cellular immune status. (6) Enhanced CMI by the transfer of sensitized T lymphocytes. A combination of immunologic techniques will be employed in these investigations. Peripheral sensitization will be determined by lymphocyte blastogenesis. T and B cells will be identified in gingival cell suspensions with specific fluoresceinated reagents. Antibody responses will be determined by an indirect ELISA technique.